diff --git a/docs/examples/ethers/index.js b/docs/examples/ethers/index.js
index f4f6f3c..fe7f5a3 100644
--- a/docs/examples/ethers/index.js
+++ b/docs/examples/ethers/index.js
@@ -1,41 +1,15 @@
-//import {ethers} from 'https://unpkg.com/ethers/dist/ethers.js'
 import {ethers} from 'https://unpkg.com/ethers@5.7.2/dist/ethers.esm.js'
 
-const URL = 'https://ethereum-goerli-rpc.allthatnode.com'
+const URL = 'https://rpc.ankr.com/eth_goerli'
 
 const p = ethers.getDefaultProvider(URL)
-await p._networkPromise
-
 
 const latest = await p.getBlock()
-latest
-
 
 const txs = await Promise.all(latest.transactions.map(t => 
   p.getTransactionReceipt(t)
 ))
 
-
-const totalGas = txs.reduce((gas,tx) => 
-  gas.add(tx.gasUsed), ethers.BigNumber.from(0))
-  
-  
-  
-  
-  totalGas.add(21)
-  
-
-/*
-const totalGas = txs.reduce((gas,tx) => 
-  gas + tx.gasUsed, BigInt(0))
-  
-  totalGas + 1
-*/
-
-  
-  
-  
-
-  
-
-  
+const totalGas = txs
+  .filter(tx => tx != null)
+  .reduce((gas,tx) => gas.add(tx.gasUsed), ethers.BigNumber.from(0))
diff --git a/src/calltree.js b/src/calltree.js
index d67c204..54c8e09 100644
--- a/src/calltree.js
+++ b/src/calltree.js
@@ -610,6 +610,7 @@ export const find_call = (state, index) => {
   if(call != null) {
     if(call.has_more_children) {
       active_calltree_node = eval_expand_calltree_node(
+        // TODO copy eval_cxt?
         state.eval_cxt,
         state.parse_result, 
         call
@@ -625,6 +626,7 @@ export const find_call = (state, index) => {
     }
   } else {
     const find_result = eval_find_call(
+      // TODO copy eval_cxt?
       state.eval_cxt, 
       state.parse_result, 
       state.calltree, 
diff --git a/src/record_io.js b/src/record_io.js
index a118a7b..a715bb6 100644
--- a/src/record_io.js
+++ b/src/record_io.js
@@ -216,13 +216,6 @@ const io_patch = (path, use_context = false) => {
 }
 
 export const apply_io_patches = () => {
-  // TODO remove, only for dev
-  // TODO test open_run_window
-  if(cxt.window.__io_patched) {
-    throw new Error('illegal state')
-  }
-  cxt.window.__io_patched = true
-
   io_patch(['Math', 'random'])
 
   io_patch(['setTimeout'])
diff --git a/src/runtime.js b/src/runtime.js
index 5800e38..7dec0a6 100644
--- a/src/runtime.js
+++ b/src/runtime.js
@@ -202,7 +202,7 @@ export const do_eval_expand_calltree_node = (cxt, node) => {
   synchronous for simplicity
 */
 export const do_eval_find_call = (cxt, calltree, location) => {
-  // TODO remove
+  // Sanity check
   if(cxt.children != null) {
     throw new Error('illegal state')
   }
diff --git a/test/test.js b/test/test.js
index 0755dd5..37141d9 100644
--- a/test/test.js
+++ b/test/test.js
@@ -2882,7 +2882,7 @@ const y = x()`
   test('async/await logs out of order timeout', async () => {
     const i = await test_initial_state_async(`
       const delay = async time => {
-        await new Promise(res => globalThis.setTimeout(res, time*10))
+        await new Promise(res => setTimeout(res, time*10))
         console.log(time)
       }
 
@@ -3091,10 +3091,8 @@ const y = x()`
   }),
 
   test('record io fetch rejects', async () => {
-    const original_fetch = globalThis.run_window.fetch
-
     // Patch fetch
-    Object.assign(globalThis.run_window, {fetch: () => Promise.reject('fail')})
+    patch_builtin('fetch', () => Promise.reject('fail'))
 
     const initial = await test_initial_state_async(`
       await fetch('url', {method: 'GET'})
@@ -3102,7 +3100,7 @@ const y = x()`
     assert_equal(root_calltree_node(initial).error, 'fail')
 
     // Patch fetch again
-    Object.assign(globalThis.run_window, {fetch: async () => 'result'})
+    patch_builtin('fetch', () => async () => 'result')
 
     const with_cache = await command_input_async(initial, `
       await fetch('url', {method: 'GET'})
@@ -3110,7 +3108,7 @@ const y = x()`
     assert_equal(root_calltree_node(initial).error, 'fail')
 
     // Remove patch
-    Object.assign(globalThis.run_window, {fetch: original_fetch})
+    patch_builtin('fetch', null)
   }),
 
   test('record io preserve promise resolution order', async () => {
diff --git a/test/utils.js b/test/utils.js
index cd11a6c..5e5ca8f 100644
--- a/test/utils.js
+++ b/test/utils.js
@@ -12,36 +12,39 @@ Object.assign(globalThis,
   }
 )
 
-export const original_setTimeout = globalThis.setTimeout
-
 export const patch_builtin = new Function(`
-  // Substitute some builtin functions: fetch, setTimeout, Math.random to be
-  // able to patch them in tests
+  let originals = globalThis.run_window.__builtins_originals
+  let patched = globalThis.run_window.__builtins_patched
+  if(originals == null) {
+    globalThis.run_window.__original_setTimeout = globalThis.setTimeout
+    // This code can execute twice when tests are run in self-hosted mode.
+    // Ensure that patches will be applied only once
+    originals = globalThis.run_window.__builtins_originals = {}
+    patched = globalThis.run_window.__builtins_patched = {}
 
-  const originals = {
-    random: Math.random,
-    fetch: globalThis.fetch,
-    setTimeout: globalThis.setTimeout,
+    const patch = (obj, name) => {
+      originals[name] = obj[name]
+      obj[name] = (...args) => {
+        return patched[name] == null
+        ? originals[name].apply(null, args)
+        : patched[name].apply(null, args)
+      }
+    }
+
+    // Substitute some builtin functions: fetch, setTimeout, Math.random to be
+    // able to patch them in tests
+    patch(globalThis.run_window, 'fetch')
+    patch(globalThis.run_window, 'setTimeout')
+    patch(globalThis.run_window.Math, 'random')
   }
 
-  const patched = {}
-
-  const patch = (obj, name) => {
-    originals[name] = obj[name]
-    obj[name] = (...args) => patched[name] == null
-      ? originals[name](...args)
-      : patched[name](...args)
-  }
-
-  patch(globalThis, 'fetch')
-  patch(globalThis, 'setTimeout')
-  patch(Math, 'random')
-
   return (name, fn) => {
     patched[name] = fn
   }
 `)()
 
+export const original_setTimeout = globalThis.run_window.__original_setTimeout
+
 export const parse_modules = (entry, modules) => 
   load_modules(entry, module_name => modules[module_name])